[0001] the following of which is a specification therefor.
BACKGROUND OF THE INVENTION
[0002] This invention deals with graphene platelet nano composites with silicon. The composited
particles are useful as electrodes and for electrical applications.
[0003] Graphite is formed by many layers of carbon in highly structured platelets. These
platelets, when separated from the graphite superstructure, are collectively called
graphene. Graphene has interesting chemical, physical, and electrical properties.
These properties make graphene a highly valued product. The quality of the graphene,
as defined by particle diameter, particle width, and surface area, determine its industrial
utility. It is advantageous to coat or composite graphene with metal particles for
electrical applications.
[0004] Xg Sciences, Inc. headquartered in Lansing, Michigan produces a "C" grade graphene
by a high energy, plastic media, dry, mechanical milling process. Grade size characteristics
make it uniquely suited to coating or mixing with nanoparticles to form useful materials
for electrodes.
[0006] Also, the patentees are aware of
EP2275385 in the name of Peukert, et al in which a wet process is set forth for grinding particulate materials, wherein the
grinding media is yttrium stabilized zirconia.
[0007] WO 2009/127901 describes a lithium metal phosphate/carbon nanocomposite as cathode material for
rechargeable electrochemical cells with the general formula LixMlyM21_yPO4/C where
Ml is Fe, Mn, Co, Ni, VF and M2 is Fe, Mn, Co, Ni, VF, Mg, Ca, Al, B, Cr, Zn, Cu,
Nb, Zr, V, Ti and x = 0.8-1.0 and y = 0.5-1.0, with a carbon content of 0.5 to 20%
by weight.
[0008] US 2009/0117467 describes a nano-scaled graphene platelet-based composite material composition for
use as an electrode, particularly as an anode of a lithium ion battery. The composition
comprises: (a) micron- or nanometer-scaled particles or coating which are capable
of absorbing and desorbing lithium ions; and (b) a plurality of nano-scaled graphene
platelets (NGPs), wherein a platelet comprises a graphene sheet or a stack of graphene
sheets having a platelet thickness less than 100 nm; wherein at least one of the particles
or coating is physically attached or chemically bonded to at least one of the graphene
platelets and the amount of platelets is in the range of 2% to 90% by weight and the
amount of particles or coating in the range of 98% to 10% by weight. Also described
is a lithium secondary battery comprising such a negative electrode (anode).
[0011] CN 102 214 817 describes a carbon/silicon/carbon nano composite structure cathode material and a
preparation method thereof, belonging to the technical field of electrochemical power
supply technologies.
[0012] EP 2 275 385 describes a method of producing from particles of a layered material platelets comprising
the layered material, wherein the particles are exposed to a mechanical grinding treatment
using grinding media, the stress energy of the grinding media SF GM being smaller
than 10 µNm. It also describes a method of producing from particles of a layered material
platelets comprising the layered material, wherein the particles are exposed to a
mechanical grinding treatment, thereby exfoliating at least some of the particles
of the layered material to produce platelets of the layered material, at least some
of the platelets thus generated being less than 4 nm thick.
SUMMARY OF THE INVENTION
[0013] Graphene produced by media ball milling has very small particle size with a relatively
high surface area. It is uniquely suited to make nano-composites or coatings by coating
or admixing other particles. Metals or metal oxides can be coated or formed into composites
with the high surface area, relatively low aspect ratio graphene. It is believed by
the inventors herein that the materials of this invention have unique aspect ratios.
Ground graphite admixed with silicon has an aspect ratio fairly close to 1, graphene
from a GO process, epitaxially grown graphene, or graphene from an intercalated -
heating process has a very high aspect ratio. The moderate aspect ratio graphene of
this invention better coats 1 to 4 micron particles and better mixes with even small
nanoparticles.
[0014] Based on Raman spectroscopy with the aspect ratio, particle size, and/or surface
area, provides graphene in this invention that is unique.
[0015] Based on the following table calculated from Raman Spectroscopy and measuring peak
height, generated the following table.
m2/g |
G |
D |
G/D |
Gpeak |
250 |
50 |
5 |
10 |
1580 |
400 |
19 |
6 |
3.2 |
|
500 |
21 |
7 |
3 |
|
600 |
16 |
6 |
2.7 |
1585 |
[0016] Native graphite has a very high G/D ratio. Graphite ground to amorphous powder has
the G/D ratio. the material of the instant invention starts high and tends toward
2 the more the material is processed. Amorphous graphite also has a G peak red shift
to 2000 cm
-1. The material of the instant invention may have a small red shift, but from the quality
of the data it is hard to determine. The very high surface area and aspect ratio confirms
it is largely graphene nano-platelets.
[0017] Mechanically exfoliated graphene is distinct from ground graphite, in that, it maintains
the strong crystalline sp2 structure. As graphite is ground to amorphous, the ratio
of G to D Raman lines tends to 2 and the G line red shifts from 1560 cm
-1 to 2000 cm
-1. The G peak is referred to as the graphene peak. The D peak referred to as the Disorder
peak. The more graphite is ground, the more the G peak is reduced and the D peak is
increased.
[0018] If the added particles are larger than the graphene, they are coated with graphene,
and if they are about the same approximate size, a nano-composite forms. The nanocomposites
are useful for producing electrodes, especially for battery and capacitor applications.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Figure 1 is a graph of battery performance of a Si/graphene (200-250 m
2/g, 100 minutes processing time).
THE INVENTION
[0020] Thus, in the present invention, there is a process of dry milling particulate materials,
the process comprising: dry milling the particulate materials with a plastic milling
media having a hardness on the Brinell Scale in the range of 3 to 100; wherein at
least one of the particulate materials is a layered material of graphite, in the presence
of a non-layered material of silicon; wherein the milling media has a surface energy
equivalent to the surface energy of the layered material; wherein the dry milling
exfoliates the layered material to obtain an exfoliated material of graphene having
a particle size of 10 microns to 5 nm thick, or less, and an aspect ratio of from
5 to 200; and wherein the dry milling composites the non-layered material with the
exfoliated material.
[0021] The exfoliated material has a particle size of 10 microns by 5 nm thick, or less.
In addition, the dry milling is controlled by controlling the surface energy of the
milling media in addition to controlling the hardness of the milling media.
DETAILED DESCRIPTION OF THE INVENTION
[0022] The graphene produced by the methods of this invention has a relatively narrow aspect
ratio, greater than graphite. For this invention aspect ratios above 5 and below 200
are part of the invention and preferred are aspect ratios above 10 and below 25.
[0023] The small, that is, 1 to 5 nanometers thick, and 50 to 100 nanometers diameter, high
surface area (above 500 BET), medium aspect ratio graphene, is a unique size for coating
with small metal or metal oxide particles.
[0024] The metal used in this invention is the metalloid silicon. Other useful metals are
the the metals tin, iron, magnesium, manganese, aluminum, lead, gold, silver, titanium,
platinum, palladium, ruthenium, copper, nickel, rhodium, and alloys of any of the
above.
[0025] The plastic milling media used in this invention has a hardness on the Brinell Scale
in the range of 3 to 100. The plastic milling media is selected from the group consisting
essentially of polyacetals, polyacrylates, such as, for example, methylmethacrylate,
polycarbonate, polystyrene, poly- propylene, polyethylene, polytetrafluoroethylene,
polyethylene- imide, polyvinylchloride, polyamine-imide, phenolics and formaldehyde-based
thermosetting resins, and alloys of any of the plastics named.
[0026] Useful particulate metal oxides aremetal oxides selected from silicon, tin, iron,
magnesium, manganese, aluminum, lead, gold, silver, titanium, platinum, palladium,
ruthenium, copper, nickel, rhodium, tungsten, cobalt, molybdenum, and alloys of any
the above named metal oxides, wherein the metal and metal oxide particles have a size
of 100 microns or less. Preferred are particle sizes of 10 microns or less, and most
preferred are particle sizes of 5 microns or less.
[0027] Metal carbides, metal nitrides are useful in this invention, as well as non-layered
materials.
[0028] Graphene useful in this invention has a thickness of 5 nm or less.
Examples
Example 1
[0029] Two grams of natural graphite and 1 g of micron sized Si (1 to 4 um) were loaded
into a 65 ml stainless steel grinding container and milled in the presence of 24 g
of polymethylmethacrylate balls. The polymethylmethacrylate balls consisted of two
different sizes, namely, 1/4 inches and 3/8 inches in diameter. The high energy milling
machine was operated at < 1500 rpm and its clamp speed was 1060 cycle/min. The polymethylmethacrylate
balls can be replaced with polycarbonate, polystyrene, polypropylene, polyethylene,
polytetrafluoroethylene, polyethyleneimide, polyvinylchloride and polyamide-imide
to control milling efficiency, graphene size, porosity distribution and surface area
at a fixed milling time, contact quality between Si and graphene surface. The surface
area of the Si/graphene composite produced can be varied from 100m
2/g to 700m
2/g depending on milling time (60 to 500 min.) and Si/graphene composition and type
of ball materials.
[0030] The result for the battery performance of a Si/graphene (200 to 250 m
2/g, 100 min. processing) sample as an anode for a lithium ion battery is plotted
infra. The Si/graphene shows high capacity (>800 mAh/g, electrode loading) over 35 cycles
at 100 mA/g, which supports the low cost, simple, time-saving, environmentally benign,
flexible way to produce high performance graphene-based composite materials for energy
applications. Some fluctuation of the capacity is due to the variation of temperature.
Reference Example 2
[0031] Two grams of natural graphite and 1 g of nano sized metal oxides (Fe
2O
3, NiO, CoOs, MnO
3) were loaded in a 65 ml stainless steel grinding container and milled in the presence
of 24 g of polymethylmethyacrylate balls. The products can be used as anode materials
for lithium batteries and electrodes for supercapacitors.
1. A process of dry milling particulate materials, the process comprising:
dry milling the particulate materials with a plastic milling media having a hardness
on the Brinell Scale in the range of 3 to 100;
wherein at least one of the particulate materials is a layered material of graphite,
in the presence of a non-layered material of silicon;
wherein the milling media has a surface energy equivalent to the surface energy of
the layered material;
wherein the dry milling exfoliates the layered material to obtain an exfoliated material
of graphene having a particle size of 10 microns by 5 nm thick, or less, and an aspect
ratio of from 5 to 200;
and wherein the dry milling composites the non-layered material with the exfoliated
material.
2. The process as claimed in claim 1 wherein the exfoliated material has an aspect ratio
of greater than about 25;
or
wherein the exfoliated material has a size in the range of from 50 nm to 10 microns;
or
wherein the exfoliated material has a thickness of from 1 nm to 5 nm.
3. The process as claimed in claim 1 wherein the plastic is selected from the group consisting
of:
i. polymethylmethacrylate,
ii. polycarbonate,
iii. polystyrene,
iv. polypropylene,
v. polyethylene,
vi. polytetrafluoroethylene,
vii. polyethyleneimide,
viii. polyvinylchloride,
ix. polyamine-imide, and,
x. alloys of any of i. to ix.
4. The process as claimed in claim 1 wherein the particulate non-layered material has
a size less than 100 microns.
1. Verfahren zum Trockenmahlen von teilchenförmigen Materialien, wobei das Verfahren
Folgendes umfasst:
Trockenmahlen der teilchenförmigen Materialien mit einem Kunststoffmahlmedium mit
einer Härte auf der Brinell-Skala in dem Bereich von 3 bis 100;
wobei zumindest eines der teilchenförmigen Materialien ein geschichtetes Material
aus Graphit in der Gegenwart eines nicht geschichteten Materials aus Silizium ist;
wobei das Mahlmedium eine Oberflächenenergie äquivalent zu der Oberflächenenergie
des geschichteten Materials aufweist;
wobei das Trockenmahlen das geschichtete Material abblättert, um ein abgeblättertes
Material aus Graphen mit einer Teilchengröße von 10 Mikrometern mal 5 nm Dicke oder
weniger und einem Seitenverhältnis von 5 bis 200 zu erhalten;
und wobei das Trockenmahlen das nicht geschichtete Material mit dem abgeblätterten
Material verbindet.
2. Verfahren nach Anspruch 1, wobei das abgeblätterte Material ein Seitenverhältnis von
mehr als etwa 25 aufweist;
oder
wobei das abgeblätterte Material eine Größe in dem Bereich von 50 nm bis 10 Mikrometern
aufweist;
oder
wobei das abgeblätterte Material eine Dicke von 1 nm bis 5 nm aufweist.
3. Verfahren nach Anspruch 1, wobei der Kunststoff ausgewählt ist aus der Gruppe bestehend
aus:
i. Polymethylmethacrylat,
ii. Polycarbonat,
iii. Polystyrol,
iv. Polypropylen,
v. Polyethylen,
vi. Polytetrafluorethylen,
vii. Polyethylenimid,
viii. Polyvinylchlorid,
ix. Polyaminimid, und
x. Legierungen von einem beliebigen von i. bis ix.
4. Verfahren nach Anspruch 1, wobei das teilchenförmige nicht geschichtete Material eine
Größe von weniger als 100 Mikrometern aufweist.
1. Procédé de broyage à sec de matériaux particulaires, le procédé comprenant :
le broyage à sec des matériaux particulaires avec un agent de broyage en plastique
comportant une dureté sur l'échelle Brinell dans la gamme de 3 à 100 ;
dans lequel au moins l'un des matériaux particulaires est un matériau stratifié de
graphite, en présence d'un matériau non stratifié de silicium ;
dans lequel l'agent de broyage comporte une énergie de surface équivalente à l'énergie
de surface du matériau stratifié ;
dans lequel le broyage à sec exfolie le matériau stratifié pour procurer un matériau
exfolié de graphène comportant une taille de particule de 10 microns sur 5 nm d'épaisseur
ou moins, et un rapport de forme de 5 à 200 ;
et dans lequel le broyage à sec forme un composite du matériau non stratifié avec
le matériau exfolié.
2. Procédé selon la revendication 1, dans lequel le matériau exfolié comporte un rapport
de forme supérieur à environ 25 ;
ou
dans lequel le matériau exfolié comporte une taille dans la gamme de 50 nm à 10 microns
;
ou
dans lequel le matériau exfolié comporte une épaisseur de 1 nm à 5 nm.
3. Procédé selon la revendication 1, dans lequel le plastique est sélectionné dans le
groupe constitué de :
i. polyméthacrylate de méthyle,
ii. polycarbonate,
iii. polystyrène,
iv. polypropylène,
v. polyéthylène,
vi. polytétrafluoroéthylène,
vii. polyéthylèneimide,
viii. chlorure de polyvinyle,
ix. polyamine-imide, et
x. des alliages d'éléments quelconques de i à ix.
4. Procédé selon la revendication 1, dans lequel le matériau particulaire non stratifié
comporte une taille de moins de 100 microns.